The use of GPS in aircraft applications provides a
necessary update for landing systems, but the low power
levels used in GPS leave aircraft susceptible to
unintentional interference in the GPS frequency bands.
Determining the location of unintentional interference
sources and removing them is becoming important for
both civilian and military aircraft. The focus of the
research and development work described in this paper is
to use COTS anti-jam hardware instead of expensive
custom equipment to perform the direction finding task.
In addition to providing the information necessary to
determine the direction of arrival of the interference
source, the anti-jam equipment will also protect a GPS
receiver from the interference. Position information from
this GPS receiver can then be used in combination with
the direction of arrival information to locate the
interference source.
Our objective is to use analysis, simulation, and
laboratory testing to show that direction finding can be
performed using a four element digital adaptive spatial
filter. Direction finding performance was measured using
simulations to compare square and triangular antenna
array geometries, and direction finding algorithms.
Direction finding algorithms include: (1) searching for
nulls based on the ASF weights, (2) a monopulse
technique, and (3) a simplified MUSIC (MUltiple SIgnal
Classification) technique. Results show that the ease of
implementation as well as performance is determined by
the combination of array geometry and algorithm. A
triangular antenna geometry works better with weight
based techniques, while a simplified version of the
MUSIC algorithm is easier to implement on a square
array. The results presented in this paper suggest that an angle of arrival accuracy of ±2 degrees with COTS
hardware employing these algorithms can be obtained.